Process for producing a petroleum base pitch



United States Patent Maine No Drawing. Filed Sept. 11, 1957, Ser. No. 683,224 4 Claims. (Cl. 208-22) This invention relates to a method of producing a petroleum base pitch and more particularly to the production of a novel petroleum base pitch having physical characteristics more comparable to coal tar pitch than conventional petroleum asphalts and pitches.

With the development of new applications in recent years for coal tar products there has consequently been created an increasing demand for salable coal tar pitch. However, most coal tar products plants in the United States are operated by steel companies and the pitch produced by the distillation of coal tar is utilized by these companies as fuel for their open hearth furnaces. Consequently, of the total volume of coal tar produced in the country only a very small percent is available as salable pitch. To meet the increasing demand for coal tar pitch attempts have been made to find a petroleum pitch comparable in all respects to coal tar pitch. Investigations have proved fruitless particularly in uncovering a petroleum pitch possessing the low needle penetration, low molten viscosity and high insolubility in benzene, naphtha and kerosene that characterizes the coal tar pitches.

It has now been found that a homogeneous petroleum base pitch that compares favorably with coal tar pitch may be produced by heating at a temperature of about 700 to about 1000 F., a feedstock composed of petroleum bottoms obtained from distilling a cracked oil produced by catalytic cracking processes. The employment of a high temperature from about 700 to about 1000 F. by itself is suflicient to produce the novel product of this invention. The effect of my novel process is the condensation or polymerization of aromatic material present in the feedstock to form higher molecular weight ring compounds that subsequently yield the pitch material of this invention. A petroleum pitch produced in this manner is found to exhibit physical characteristics markedly similar to those of coal tar pitch. In addition to high insolubility in benzene and petroleum naphtha, the pitch displays low penetration and low molten viscosity.

The feedstock of my invention must possess certain specific properties to yield a suitable pitch. An ideal feedstock would be composed substantially completely of aromatic ring compounds with little or very slight side chain substitution and a minimum molecular weight of 190. However, all commercially available fee'dstocks contain other components such as paraflins and non-reactive naphthenes and aromatics which tend to hinder pitch production and should for that reason be removed as a part of the processing sequence. If the latter materials are not removed, a non-homogeneous, valueless material is produced.

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Feedstocks suitable for this process are characterized by the following approximate properties:

Gravity, API (ASTM D287-55) 18.0 max. Flash, F. ASIM D92-52) 5 Average mo ecular weight- Initial boiling point, F Chromatographic analysis:

saturates, Wt. percent 50 max. Aromatics andpolar compounds, wt. percent 50 min. Aromatic fraction- Average moelcular Weight 190 min. Hazelwocd ring analysis:

Average No. of rings per molecule 3.5 min. Average No. of aromatic rings per molecule 3.0 min. Average N o. of naphthemc rings per molecule structure 1.0 max. Average No. of carbon atoms in aromatic ring structure 13.0 min; Average No. of carbon atoms in naphthenic rings and parafin side chain structures 5.0 max.

A petroleum refinery stock found to meet all of these requirements and yield a suitable pitch is the bottoms fraction obtained by the distillation of the cracked oil produced from the catalytic cracking of petroleum gas oils in the presence of catalyst such as the silica-alumina catalysts. In such processes the catalyst usually comprises about 65 to 95% silica and 5 to alumina and is frequently employed in the fluidized state.

The cracked oil produced as a result of the fluid catalytic cracking process is then subjected to distillation at about 7 to 25 psi. pressure to a maximum temperature of about 650 to 750 F. The residue or distillation bottoms obtained as a consequence of the above distillation process are transferred to a slurry settler for removal of catalyst and the resultant oil has been found to be a suitable refinery stock for the production of my novel petroleum base pitch. This petroleum bottoms fraction will be hereafter referred to as fluid unit clarified oil and the novel petroleum base pitch produced as clarified oil pitch. Although the present invention will be described with reference to the employment of fluid cracking unit clarified oil as the suitable feedstock, any petroleum feedstock meeting the property requirements set forth above may be used. Typical tests on satisfactory fluid unit clarified oils are shown below:

Tests on Olariilfied o Gravity, API (ASTM D287-55) 4. 5-12. 5 Flash, F. (ASTM D92-52) Fire, a r. (ASIM D92-62) Viscosity at 210 F., SSU (ASTM D88-53) Aniline point, C. (AS'IM D611-65T). Molecular Weight Boiling range (90% distilled), F Chromatographic analysis:

Paraffins, wt. percent 23. 0-38. 0 Polar compounds, wt. percent 2. 0-2.0 Aromatics, wt. percent 75.0-60.0 Tests on aromatic fraction- Reiractive index, 20/D Density, 20/4 O Molecular weight Hazelwood ring analysis:

Average No. of rings per molecule- Average No. of aromatic rings per molecule.. .6 Average No. of carbon atoms or molecule 20. -19. 0 Average No. of carbon atoms in ring structure. 19. 6-18. 2 Average No. of carbon atoms in aromatic ring structure 16. 8-16. 2

Chromatographic analyses of various fluid unit clarified oil feedstocks show them as characterized by an aromatic content ranging from 50 to weight percent of these feedstocks; best yields being obtained from those possessing the highest aromatic content. The aromatic content of the clarified oils has been found to be dependent to some degree on fluid unit conversion levels (yield of 400 RP. gasoline). For example, at 78.5% conversion pitch yield from the resultant clarified oil is 59.0%; whereas at 60% conversion yield is 45.0%. Generally speaking, the cracking unit must be operated at a minimum 50% conversion (50% yield of 400 BR gasoline) to yield a clarified oil that is an economical feedstock for my process.

Although a large variation is found in the aromatic content of the many fluid unit clarified oils, ring analyses of the aromatic fractions from both the clarified oils and their respective distillation cuts indicate very slight diffcrences in composition. The average molecular structure by Hazelwood Ring Analyses, Analytical Chemistry, 26, 1073 (1954), of the aromatic fractions from clarified oils has been found to contain about 3.5 to 3.7 aromatic rings, 0.4 to 0.7 naphthenic ring, and 0.5 to 1.3 carbon atoms attached to the ring structure. Thus, the. aromatic fractions are characterized as containing condensed ring molecules with slight side chain substitutions.

In carrying out the present invention a clarified oil meeting the property requirements set forth above is subjected to temperatures of about 700 to 1000 F., preferably about 750 to 800 F., for a period of at least about 10 hours. No particular advantage has been associated with heating time over about 50 hours but longer periods could be employed. Preferably, the heating'time is about 10 to 20 hours. During this heating period substantially all of the non-reactive or unreactive wax-oil components in the clarified oil are removed as an overhead product. A petroleum base pitch is formed which exhibits low solubility in petroleum solvents, low molten viscosity and low needle penetration at 77 F. Although the majority of the undesirable unreacted material is taken overhead by virtue of the high processing temperatures, supplemental means such as steam stripping, vacuum distillation or solvent deoiling can be used to remove additional unreacted material.

The following example will further illustrate my invention, but it is not to be considered limiting.

EXAMPLE Specific gravity, 77/77 F 1.1490 Softening point (B. & 13.), F 204 Needle penetration at 77 F--. Vlscosity at 350 F., SELF.-- 105 Sulfur, wt. percent Insolubles in 86 naphtha, wt. percent 91. 9

Insolubles in benzene, wt. percent 40. l Tests on typical overhead oil cut:

Gravity, API 26. 1

Viscosity at 100 F., SSU 38. 6

As shown in Table I below, there is a marked similarity between coal tar pitch and the clarified oil pitch produced by the process of my invention.

Table l COMPARISON OF THE'PHYSIOAL PROPERTIES OF CLARI- FIED OIL PITCH, COAL TAR PITCH AND BLOWN ASPHALT Clarified Goal Tar Blown Oil Pltch Pitch Asphalt 1. 1490 1. 1095 1. 0190 204 187 178 0 0 26 3 2 49 4 .37 164. 9 Viscosity at 350 F SFS 105 34 199.6 Insolubles in benzene, wt. percent- 40. 1 36. 9 0. 4 Insol bles i.n 86 naphtha, wt. Percent 91. 9 94. 83.0

2,992,181 V J .i

The pitch yielded by my invention exhibits high insolubility in petroleum fractions, vegetable oils and aromatic solvents as compared to normal petroleum asphalts and pitches. The pitch gives about a 5% maximum overhead when distilled to 640 F. and preferably this is about 1%. These physical characteristics make it particularly suitable for use as a fuel resistant airport paving cement, a fuel resistant pipe coating enamel, a fiber pipe impregnant, a saturant for weatherboard, siding and insulating board, a rubber plasticizer, a sandmold binder, a molding compound, an additive for paints and a waterproofing compound. The clarified oil pitch of the invention is not limited to the above applications but may also be employed anywhere coal tar pitch has been used or wherever its novel physical properties offer advantageous results.

I claim:

1. A process for producing a petroleum base pitch which comprises heating for about 10 to 50 hours at a temperature of about 700 to 1000 F. a petroleum bottoms feedstock obtained from the distillation of the cracked oil produced by the catalytic cracking of pa troleum gas oils, said feedstock having the following approximate properties:

Gravity, API (ASIM D287-55) 18.0 max. Flash, F. (ASTM D92-52) 200mm. Average molecular weight 190 min. Initial boiling point, F 400mm. Chromatographic analysis:

saturates, Wt. percent 50 max. Aromatics and polar compounds, wt. percent 50 min. Aromatic fraction- Average molecular weight 190 min. Hazelwood ring analysis:

Average No. of rings per molecule 3.5 min. Average No. of aromatic rings per molecule 3.0 min.

1.0 max.

Average No. of naphthenic rings per molecule Average No. of carbon atoms in aromatic ringstructure 13.0 min. Average No. of carbon atoms in naphthenlc rings and paraflin side chain structures 5.0 max.

References Cited in the file of this patent UNITED STATES PATENTS 2,029,288 Bray Feb. 4, 1936 2,626,892 McCulley et la. Jan. 27, 1953 2,658,857 Roediger Nov. 10, 1953 2,752,290 'Beattie June 26, 1956 2,763,602 Cole Sept. 18,. 1956 2,764,527 Steele et al. Sept. 25,, 1956 2,796,388 Beuther et al. June 18, 1957 

1. A PROCESS FOR PRODUCING A PETROLEUM BASE PITCH WHICH COMPRISES HEATING FOR ABOUT 10 TO 5 HOURS AT A TEMPERATURE OF ABOUT 700 TO 1000*F. A PETROLEUM BOTTOMS FEEDSTOCK OBTAINED FROM THE DISTILLATION OF THE CRACKED OIL PRODUCED BY THE CATLYTIC CRACKING OF PETROLUM GAS OILS SAID FEEDSTOCK HAVING THE FOLLOWING APPROXIMATE PROPERTIES: 